Eukaryotic initiation factor 4E (eIF4E) is a 24 kDa protein that plays a key role in the initiation of translation of mRNA. At the initiation of mRNA translation, eIF4E binds to the 7-methylguanosine cap at the 5′ end of mRNAs, and forms a complex (called eIF4F) with the scaffolding protein eIF4G and the helicase eIF4A. The formation of this complex is required for the initiation of cap-dependent translation of mRNAs and therefore the binding of eIF4E to eIF4G is a critical event in this process.
eIF4E has been identified as a promising target in the field of oncology because of a number of pieces of evidentiary data that implicate its essential role in transformation and tumorigenesis. For example, overexpression of eIF4E in transgenic mice promotes tumor formation (see Silvera, D. et al. Nat. Rev. Cancer 2010, 10, 254-266 and references cited therein; see also Konicek, B. W. et al. Cell Cycle 2008, 7, 2466-2471 and references cited therein). Overexpression of eIF4E has been observed in a variety of human cancers including breast, lung, skin, colon, prostate, and cervical cancers, and is associated with poor prognosis and decreased survival (see for example, Zhou, S. et al. BMC Cancer 2006, 6, 231). Expression of eIF4E is associated with disease progression in endometrial cancer, and siRNA knockdown of eIF4E inhibits cell growth in endometrial cancer cells (Choi, H. C. et al. J. Cancer Res. Clin. Oncol. 2011, 137, 463-469). A helically stabilized peptide based on the sequence of eIF4G binds to eIF4E, and also shows inhibition of cap-dependent translation in a reporter gene assay in MCF-7 cells, although at a high concentration (Brown, C. J. et al. J. Mol. Biol. 2011, 405, 736-753). A set of peptides that bind to eIF4E and cause apoptosis in chronic lymphocytic leukemia cell lines has been disclosed in a patent application (Cosson, B. et al. WO 2010100351).
Small molecule inhibitors of the eIF4E-eIF4G interaction have been disclosed by Gerhard Wagner and colleagues (Moerke, N. J. et al. Cell 2007, 128, 257-267). The activity of these compounds has been demonstrated in vivo in a rat model of fear consolidation, which depends on the formation of the eIF4F complex (Hoeffer, C. A. et al. Proc. Nat. Acad. Sci. USA 2011, 108, 3383-3388). A number of small molecule inhibitors of the eIF4E-eIF4G interaction have been disclosed also by Min and colleagues as part of the NIH Molecular Libraries Program (HTS for inhibitors of Eukaryotic Translation Initiation, Probe Report by J. Min, Grant Number 1 R03 MH081216-01, Probe PubChem Compound Identifier: 16195554, Jun. 23 2009).
A series of eIF4E antagonists that bind to the cap binding site of eIF4E has been disclosed by Carston Wagner and colleagues (Jia, Y. et al. Eur. J. Med. Chem. 2010, 45, 1304-1313 and Jia, Y. PhD dissertation, University of Minnesota, January 2011; AN 2011:418548). Additional compounds that bind to the m7-GTP site were disclosed at the 240th National Meeting of the American Chemical Society (Aug. 22-26, 2010) (see Kopecky, D. et al. MEDI-227; abstracted in Chemical Abstracts as AN 2010:1011833). Further compounds that bind to the m7-GTP site were disclosed in patent application (Brown, C. J. WO 2010138084).
Because eIF4E is a cytosolic target, a peptide- or small molecule-eIF4E antagonist requires that the compound be delivered in the cytosol, for example by crossing the cell membrane by passive diffusion or through some active mechanism such as endocytosis. However since most peptides are not cell-penetrating, this is a challenge for peptide-based antagonists.
Cell-penetrating peptides (CPPs) are a class of peptides with the ability to convey various, otherwise impermeable, macromolecules across the plasma membrane of cells in a relatively non-toxic fashion. The CPP peptides are typically between 5 and about 30 amino acids (aa) in length with a cationic, amphipathic, or hydrophobic nature. Notable examples of cell-penetrating peptides include Tat, Penetratin, and Transportan. (Fawell, S. et al. Proc. Natl. Acad. Sci. 1994, pp 664-668; Theodore, L. et al. J. Neurosci. 1995, pp 7158-7167; Pooga, M. et al. FASEB J. 1998, pp 67-77). A cell penetrating peptide such as Tat can be attached to an effector peptide, or the effector peptide can be intrinsically cell-penetrating. Examples of effector peptides intrinsically cell-penetrating include Arf(1-22) and p28, among others (Johansson, H. J. et al. Mol. Ther. 2007, 16(1), pp 115-123; Taylor, B. N. et al. Cancer Res. 2009, 69 (2), pp. 537-546)
The present invention generally relates to peptides that are cell-penetrating and with the ability to bind to eIF4E and disrupt the eIF4E-eIF4G interaction, and to enter a tumor cell line.